Elevator control system



Dec. 17, 1935. W. F EAMES 2,024,725

ELEVATOR CONTROL SYSTEM Filed April 16, 1935 2 Sheets-Sheet 1 V @ig 5,3

WITNESSES: INVENTOR f@ MV//amffome W u ATT Dec. y17, 1935.

W. F. EAMES ELEVATOR CONTROL SYSTEM Filed April 16, 1935 WITNESSES; 2g f /gf 4.

2 Sheets-Sh AT RNEY Patented Dec. IS7, 1935 UNITED STATES PATENT OFFICE ELEVATOR CONTROL SYSTEM Application April 16, 1935, Serial No. 16,592

11 Claims.

My invention relates, generally, to electric elevator systems, and it has particular relation to control systems therefor.

In the operation of high-speed elevator systems, many operating conditions are amplified to a degree which introduces disturbing factors that are not present in lower speed elevator systems. For example, the kinetic energy of the greater portion of the moving parts of an elevator system capable of operating an elevator car at 1200 feet per minute is four times the corresponding kinetic energy of an elevator system capable ci operating an elevator car at 600 feet per minute. When a car operating under overhauling load conditions at a speed in the neighborhood of 1200 feet per minute is to be stopped with an accuracy of a small fraction of an inch of a floor level, the kinetic energy of the system must be dissipated with a minimum of disturbance in the functioning of the system, so that the desired accuracy of landing may be attained.

The overhauling load conditions exist when the car is moving in the down direction and is heavily loaded, or is moving in the up direction and is lightly loaded. Under the heavily loaded conditions, the car and its load overbalances the friction of the system and the effect of the counterweights, and literally provides a driving force which causes the dynamo-electric device having driving connection with the elevator car to function as a generator, thereby returning power tov the power source, which is otherwise used for supplying the necessary energy for operating the eleva-ter car. In like manner, when the car is moving in the up direction with a light load, the elect of the counterweights more than overbalances the weight of the car and the friction of the system, and again power is returned to the power source. Such action is highly desirable from an operating standpoint, since this dynamic braking action relieves the mechanical braking system cf a certain amount of the braking force which it would otherwise have to exert. Furthermore, it provides a degree of flexibility in braking the speed of the car, which would not otherwise be possible when the usual type of mechanical brake construction is employed. This dynamic braking acticn is especially apparent when the car is decelerating from full speed to the speed which is necessary in order to land at a floor With the desircd degree of accuracy.

In crder to operate a high-speed elevator sysa generator field control or variable voltage system is employed in which a hoisting dynamoelectric device is mechanically coupled to the car by means of the usual cable and sheave arrangement and rotates with it in its movement in the hatchway. A driven dynamo-electric device is electrically connected to the hoisting device. Separately excited iield windings are provided in each of the dynamo-electric devices for controlling the operation thereof. The lield winding for the hoisting device is invariably energized at a substantially constant Value, and the field structure with which it is associated is arranged to be saturated so that the actual voltage applied to this field Winding may be varied somewhat without aiiecting the elective eld strength. The control of the system is effected by varying the excitation applied to the driven dynamo-electric l5 device. By changing and reversing such excitation, the speed and direction of movement of the elevator car may be varied and reversed. The driven dynamo-electric device is mechanically coupled to a driving dynamo-electric device which is electrically connected to be energized from a power source.

The elevator car is brought up to running speed from standstill by increasing the excitation applied to the field structure of the driven dynamoelectric device. Under starting conditions for movement of the car, for example in the up direction, under heavy load conditions, the driven dynamo-electric device functions as a generator while the hoisting dynamo-electric device functions as a motor. Power for operating the system is then obtained by means of the driving dynamoelectric device from the power source and is translated into mechanical energy through the agency of the driven dynamo-electric device and the hoisting dynamo-electric device.

When the elevator car is moving in the downward direction under similar conditions, due to the fact that the car and load may overbalance the eiect of the counterweights and the friction of the system, the functioning of the dynamoelectric devices is reversed, that is, the hoisting dynamo-electric device functions as a generator and causes the driven dynamo-electric device to function as a motor. It, in turn, causes the driving dynamo-electric device to cease functioning as a motor and if suiiicient overhauling load is present in the system, the driving dynamo-electric device will function as a generator and will return power to the power system.

In like manner, when a lightly loaded car is started to move in the down direction, it is necessary to lift the counterweights. The hoisting dynamo-electric device then functions as a motor, While the driven dynamo-electric device functions as a generator, drawing power from the power source through the driving dynamo-electric device to supply the necessary energy for lifting the counterweights and permitting the lightly loaded car to move in the down direction. Likewise, when the elevator car is moving upwardly under these conditions, the functioning of the dynamoelectric device is reversed, due to the overhauling load which is pro-vided by the counterweights, and aga-fn power is returned to the power source.

When bringing the elevator car to a stop while it is operating under overhauling load conditions, the generator` action of the hoisting dynamoelectric device, the motoring action of the driven dynamo-electric device, and the-generator action of the driving dynamo-electric device are greatly increased over the corresponding action'when the elevator car is opeating at full speed. This increase in dynamic braking action is due to the relatively great kinetic energy in the moving parts of the elevator system, which kinetic energy must be dissipated from the system in order to bring the car to rest. Under these conditions, a considerable amount of power is returned to the power source. The power which is returned to rthe power source represents a portion of the kinetic energy which it is necessary to remove from Vthe systeminorder to decrease the speed of the elevator car from its high operating speed to landing speed.

The driving dynamo-electric device usually comprises a polyphase induction motor which is connected for energization to a source of alternating current. Under overhauling load conditions in the elevator system, this device functions as a synchronous generator and returns alternating-current power to the power source. In so doing, its speed necessarily increases from that at which it operates when it functions Yasa motor. This increase in speed is often of the order of 10% of the synchronous speed of the driving dynamoelectric device.

In order to provide an entirely independently operating power unit for each elevator car in a bank of elevators, an individual driving dynamoelectric device isprovided for each. In addition, a separate direct-current source is provided for energizing the separately excited eld windings. This source comprises a self-excited direct-current exciter-generator, which is 'mechanically coupled to be driven yby the driving dynamoelectric device. In practice, a common shaft may be provided for the exciter-generator, the driving dynamo-electric device, and the -driven dynamoelectric device. Thus, any speed changes inthe driving and driven dynamo-electric devices are reiiected in corresponding speed changes in the operation of the `exciter-generator.

Under operating conditions at full speed of 1200 feet per minute, the voltage which is applied to the hoisting dynamo-electric device by the driven dynamo-'electric device may be of the order of 366 volts. In order to stop the elevator car at a floor with the desired rdegree of accuracy, it is necessary to reduce the speed of the car to a landing speed, which may be of the order of 25 feet per minute. At this speed, the voltage which is applied to the hoisting dynamo-electric device may be of the order of 6 volts. This voltage change is effected entirely -by reducing the excitation which is applied to the separately excited field winding of' the driven dynamoelectric device. Since the separately excited field winding of the driven dynamo-'electric device is energized from the exciter-generator, it is'essential that the voltage which is available for this excitation be maintained at a predetermined value, that is, slight changes in the voltage which is available for energizing the separately excited eld winding of the driven dynamo-electric device will materially affect the low voltage which is applied to the hoisting dynamo-electric device. A change of 10% in the speed of the excitergenerator causes a corresponding change in the voltage which is applied for energizing the field winding of the driven dynamo-electric device. Under overhauling load conditions, this variation -in exciter-generator voltage caused by increase in speed of the'driving dynamo-electric device increases the excitation voltage which is applied to the separately excited field winding of the driven dynamo-electric device, and thereby decreases the `dynamic braking action afforded by this system. Therefore, the speed of the elevator car is not reduced to the desired landing speed. For instance, dueto the-cumulative action of high exciter-generator voltage during the deceleration period, a landing speed of 50 feet per minute may result rather than the desired landing speed of 25 feet per minute. The car will then overshoot the floor, and will be stopped by means of the mechanical braking system under conditions Vwhich will apply a severe shock to the elevator .car and passengers. It is, therefore, desirable to provide for maintaining the voltage of the exciter-generator available for energizing the field winding of the driven dynamo-electric device at a constant value, regardless of speed changes in its operation.

'Ihe object of my invention, generally stated, is to provide an elevator control system which shall be simple and erlicient in operation, and which may be readily and economically manufactured and installed.

The principal object of my invention is to provide for maintaining the voltage available for exciting the neld winding of the driven dynamoelectric device of a variable voltage elevator system at a constant value, regardless of the load conditions under which'the system is operating.

Another important object of my invention is to provide, in an elevator system of the variable voltage type, a compensating relay connected to be responsive to the voltage of an excitergenerator adapted to be driven with the driven dynamo-electric device, and disposed to maintain the voltage of the exciter-generator at a predetermined value, regardless of fluctuations in speed of the exciter-generator caused by variations in load conditions on the elevator system.

Other objects of my invention will, in part, be obvious, and, in part, appear hereinafter.

Accordingly, my invention is disclosed in the embodiment hereof shown in the accompanying drawings, and comprises the features of con- 00 Cil partly in section, of a compensating relay used in practicing my invention;

Fig. 3 is a lay-out of a floor selector illustrated in Fig. 2;

Fig. 4 is a diagrammatic representation of the circuits which may be used in practicing my invention; and

Fig. 4A is a view which is associated with Fig. 4 and shows the relative location of the various contact members and operating windings illustrated in Fig. 4.

According to my invention, I provide an elevator system of the generator field control or variable voltage type, organized as set forth hereinbefore. With a view to maintaining the voltage of the exciter-generator independent of. variations in the speed thereof, I provide a compensating relay having operating windings connected to be responsive to the voltage -of the excitergenerator and disposed to operate contact members which are connected to vary the effective value of a resistor which is connected in series circuit relation with the shunt eld winding of the exciter-generator. The compensating relay is adjusted so as to correct during the entire possible speed range of the exciter-generator between extremes of operating conditions of the system, Therefore, a predetermined voltage is always available for energizing the eld winding the driveni dynamo-electric device, which is 'unaffected by load conditions of the elevator system.

Referring now particularly to Figs. 1 and 4 or the drawings, an elevator car, shown generally at l0, is illustrated of conventional form. The elevator car I0 may be supported for movement in a hatchway by means of a cable II, Which is passed over a sheave I2 and is suitably balanced by the counterweights I3. The sheave I2 is mounted on a shaft I4 of a hoisting dynamoelectric device I5, which is provided with an armature I6 and a separately excited field winding l1. In order to automatically stop the elevater car IU when the hoisting dynamo-electric device I5 is not energized, a brake I8 is provided having an operating winding I8W. As illustrated, the brake I8 is arranged to apply a braking force to the shaft I4 through the agency of a brake shoe and drum, the latter being mounted on the shaft I4.

A driven dynamo-electric device I9 having an armature 20, a series field winding 2I and a separately excited eld winding 22, is electrically connected as illustrated, to the hoisting dynamoelectric device I5. The driven dynamo-electric device is arranged to be mechanically coupled to driving dynamo-electric device 23, which comprises a polyphase induction motor of the squirrel-cage type, having a rotor 24 and field windings 25.

In order to supply excitation for the' ileld windings l1 and 22 and also for certain other control functions, which will be set forth hereinafter, an exciter-generator, shown generally at 26, is provided. The exciter-generator 26 comprises an armature 21, a shunt field winding 28 and a series winding 29. The provision of the excitergenerator 26 renders unnecessary the provision ci any other source of direct current for effecting the control of the elevator system and makes unnecessary the provision of any other auxiliary common power source for operating the systern.

It will be observed that the armature 20 of the driven dynamo-electric device I9, the rotor 24 of the driving dynamo-electric device 23 and the armature 21 of the exciter-generator 26, are mounted on a common shaft; 30. Therefore, any changes` in speed caused by overhauling load conditions which tend to increase or decrease the 5 speed of rotation of the shaft 30 through the variations in dynamic braking action, as set forth hereinbefore, will be reflected in corresponding changes in speed of rotation of the armature 21 of the exciter-generator. Accordingly, the volt- 10 age generated thereby will be varied.

In order to provide for adjusting the voltage generated by the exciter-generator 26, resistors 32 and 33 are provided, resistor 32 being connected in series circuit relation with the shunt eld 15 winding 28, as illustrated, While resistor 33 is arranged to be connected in parallel circuit relation therewith. The effective value of the resistance of the resistor 32 is altered by means of contact members VI and V2 of a compensat- 20 ing relay, shown generally at 34, in Fig. 2. As there illustrated, the contact members VI and V2 comprise stationary contact members 35 and 36, which may be mounted on a frame 31 in which an operating winding V may be positioned. The 25 contact members VI and V2 also includes a movable or common contact member 38, which is carried by an armature 39, pivoted at 40, and biased by means of a spring 4I, so that contact members VI are normally closed. The armature 39 30 also carries an operating winding V, which, as illustrated in Fig. 4, is connected in series circuit relation with the winding V, and the combination is connected through a resistor 42 to be responsive to the voltage generated by the exciter-generator 26. When the voltage generated by the exciter-generator 26 is below a predetermined value, the contact members VI will be closed, thereby providing maximum excitation for energizing the shunt field winding 28. When the voltage generated by the exciter-generator 25 is above a predetermined value, the contact members V2 will be closed, thereby increasing the effective value of the resistor 32, and providing a shunt path through resistor 33 to 45 lower the excitation applied to the shunt eld winding 28. Therefore, within the range of operation of the compensating relay 34, the voltage which is generated by the exciter-generator 26 will be maintained at a constant value, re- 50 gardless of changes in speed of the exciter-generator 26.

In order to stop the elevator car I0 at a floor Where a call is registered, a oor selector, shown generally at 45, is provided, which may be driven through the shaft I4, in accordance with the movement of the elevator car` IIJ. The shaft I4 is arranged to rotate a lead screw 46 through an appropriate gear reducing mechanism. As shown more clearly in Fig. 3 of the drawings, 60 the lead screw 46 is arranged to move a brush carriage 41, which carries brushes 48 and 49 for engagement with floor segments when the car moves in the down direction, and brushes 48 and 49' for engagement with oor segments 65 when the car moves in the up direction. As illustrated, the brush 48 is arranged to successively engage call pick-up segments 2PD through EPD, while brush 49 is arranged to engage call-cancelling segments 2CD through SCD. In like man- 70 ner, the brushes 48' and 49 are arranged to engage corresponding oor segments in the opposite direction of travel.

Since my invention may be practiced in connection with an elevator system having any desired number `of floors, vonly theconnections for iioors through 6 are illustrated herein. It will be understood, however, that the system may be extended to a larger number of iioors, as may be desired. Further, in order to simplify the showinfI of my invention, only the circuits associated with the iioor segments for the down direction are iiiustrated in the diagram shown in Fig. li.

'Ihe elevator car l!! is stopped at a floor where a call is registered by means of a slowdown in- Y ductor E, and a landing inductor F both or" which are carried by the elevator car. These inductors are respectively provided with normally closed contact members El, E2 and Fi, F2. When the operating windings of the inductors E and F are energized, the respective contact members thereof will be opened on moving into proximity with inductcr plates located in the hatchway and individual to each floor. Thus, as the car Hl approaches the fth oor in the down direction and the operating winding of the inductor E is energize-d, when the contact members EE come into proximity with the plate DE, they will be opened. In like manner, when the contact members F2 of the landing inductor F come into proximity with the plate DF they will be opened. Inductor plates UF and UE are provided for opening contact members Fl and Ei respectively, when the car Il is moved toward the fth floor in the up direction.

The elevator car iii is also provided with a master switch MS having three positions. When the handle of the master switch MS is moved to the right, a circuit is completed through contact member MSD for operating the elevator car lil in the down direction. When the handie is moved to the left, acircuit is completed through contact member MSU to operate the elevator car IQ in the up direction. In the center position of the master switch MS a circuit is completed for stopping the elevator car l@ at the desire oi the operator. f

In response to the operation of the master switch MS, reversing switches U and D are operated, depending upon the position to which the master switch MS is operated. The operating windings of the reversing switches U and D are arranged to be energized through the operating winding of an auxiliary relay N. The elevator car iii is brought up to full speed by the operation of a speed switch H, which at contact members HI is arranged to short circuit a resistor 5@ that is connected in series circuit relation with the separately excited field winding or" the driven dynamo-electric device i9.

Each iloor is provided with a call button individual to the direction in which it is desired to travel. Thus, the fifth floor is provided with a hall button 5U for stopping the elevator car i@ when it is moving in the up direction, and a hall button 5D for stopping it when it is movin the down direction. Only hall buttons 2D through 6D are illustrated herein, as set forth ereinbefore In response to the operation of any of the hall buttons 2D through BD, call storing relays 2DR through EDR are energized, depending upon the hall button that is operated. As illustrated, the call storing relays are provided with main operating windings and releasing windings ZDRN through SDRN. When any one of the call storing relays is energized, it is automatically locked in through its own contact members and remains in this condition until the call-cancelling brush i9 engages the corresponding call-cancelling segment to complete a circuit for energizing the corresponding neutralizing winding to overcome the flux generated by the operating winding and permit the relay to be restored to the non-operated position.

When the call pick-up brush 48 comes into contact engagement with a call pick-up segment that is energized as a result of the operation of a call storing relay, a call pick-up relay S is energized, which is provided with contact members Sl that are eective to initiate the slowdown sequence for the elevator car l0.

In order to initiate the functioning of the system, a push button switch PB is provided, which is arranged to complete a circuitfor energizing the operating winding of a starting switch A. The switch A is arranged to connect the windings 25 of the driving dynamo-electric device 23 to a source of polyphase alternating current which may be represented by the conductors 5l through starting resistors 52. As soon as the driving dynamo-electric device 23 reaches a predetermined speed, the voltage generated by the eX- citer-generator 2% is sufficient to effect the energization of the operating winding of an auxiliary starting relay B, the contact members BI, B2 and B of which are arranged to short circuit the starting resistors 52 and permit the windings 25 to be connected directly to the conductors 5i. Another function of the starting relay B is to prevent the energization of the control system until the voltage of the exciter-generator reaches a predetermined value.

In describing the operation of the elevator system, it will be assumed that the conductors 5l are connected to a suitable source of alternating current. The push button switch PB may then be depressed to complete an obvious energizing circuit for the operating winding of the starting switch A. At contact members AI, A2 and A3 thereof, obvious circuits are completed for energizing the windings 25 of the driving dynamoelectric device 23. As soon as it reaches a predetermined speed, as set forth hereinbefore, the auxiliary starting switch B is closed through contact members A4 of the starting switch A and the driving dynamo-electric device 23 then operates at full speed. At contact members B4 a circuit is completed for energizing conductors LI and L2 which are connected `to supply the necessary control energization and permit the eld winding 22 to be energized. Under the foregoing conditions, the separately excited field winding l'l of the hoisting dynamo-electric device l5 will be energized. In addition, the windings V and V of the compensating relay 3 will be energized and they will control the operation of the contact members Vl and V2 to adjust the voltage of the exciter-generator 26 to the predetermined value for which the relay 34 has been set.

It will be assumed that the car l G is at the top of the hatchway and that the operator moves the handle of the master switch MS to the right to initiate its movement in the downward direction. A circuit is then completed for energizing the operating winding of the reversing switch D' over a circuit which may be traced as follows:

LI, MS, MSD, F2, D, N, L2

The energization of the reversing switch D completes a circuit for energizing the separately eX- cited iield winding 2v2 of the driven dynamoelectric device I9, which may be traced as follows:

LI, D3, 22, DI, 50, L2

A circuit is also completed for energizing the releasing winding I 8W of the brake I8 so that it may be released:

As soon as the reversing switch D is closeda circuit is completed for energizing the operating winding of the speed switch H,

LI, D4, E2, H, L2

Contact members HI short circuit the resistor 50 and full excitation is applied to the eld winding 22. The elevator car I0 is then operated in the downward direction at full speed.

It will also be assumed that the elevator car I0 is heavily loaded so that the system is operating at overhauling load conditions. Under these conditions, as set forth hereinbefore, the hoisting dynamo-electric device I5 is functioning as a generator, while the driven dynamo-electric device I9 is functioning as a motor and drives the driving dynamo-electric device 23 and the exciter generator 26. Under these operating conditions, the speed at which the exciter-generator 2&5 is driven is such as to raise the voltage generated thereby above that which would be generated at a lower speed. As a result, the contact members V2 of the compensating relay 34 will be closed and the contact members VI thereof will be opened. It Will be understood, however, that the contact members VI and V2 may operate rapidly to vary the effective value of the resistor 32, in order to maintain the predetermined voltage which is desired.

It will now be assumed that a passenger at the fifth floor operates the down call button 5D in order to stop the elevator at that floor. As a result of the operation of the down call button 5D, the corresponding call storing relay SDR is energized:

LI, 5D, EDR, L2

This relay is maintained in the energized position by means of contact members 5DRI, which complete an obvious holding circuit around the down call button 5D. It is, therefore, unnecessary to hold the down call button 5D in the operated position.

At contact members 5DR2an obvious circuit is completed for connecting the down call pick-up segment SPD to the energized conductor LI. When the call pick-up brush 48 engages the segment EPD, an obvious circuit is completed for energizing the operating Winding of the call pickup relay S, which at contact members SI completes a circuit for energizing a holding relay J.

LI, SI, J,Nl, L2

`At contact members J I the holding relay J completes a holding circuit therefor which renders unnecessary the continued energization of the call pick-up relay S.

The operating winding of the slowdown inductor E is energized in parallel with the operating winding of the holding relay J. As soon as the contact members E2 thereof come into proximity to the inductor plate DE they are opened, and as a result, the previously traced energizing circuit for the operating winding of the speed switch H is opened and it is deenergized. As a result, the contact members HI are opened and the resistor 5U is reinserted in series circuit relation with the car IU may overshoot the oor or it may be caused to stop suddenly due to the sudden application of the brake I 8. In any event, if the speed of the car is not reduced to the predetermined land- "ing speed, the adjustments for stopping the car and levelling it at the floor will not be able to stop it under the desired conditions.

Since it has been assumed that the car I0 is carrying a heavy load so that the system is operating under overhauling load conditions, it is desirable to have the excitation of the eld winding 22 reduced to a predetermined value. However, due to the fact that the driven dynamoelectric device I9 is functioning as a motor, it will drive the rotor 24 of the driving dynamoelectric device at a higher speed in order to return more power to the alternating-current power source, which represents the kinetic energy of the system which must be dissipated. This increase in speed correspondingly causes an increase in speed of the exciter-generator 26, which, without the 4compensating relay 34, would cause an increased voltage to be applied to the eld winding 22. This increased voltage applied to the field winding 22 will reduce the motoring action of the driven dynamo-electric device I9, and as a result, the dynamic braking action provided thereby would not be as great as is the case when the excitation of the eld winding 22 is maintained at the predetermined lower value. Therefore, when the compensating relay 34 is provided, the excitation of the riad Winding 22 will be Amaintained. at the predetermined desired value,

regardless of the load conditions of the system and speed changes of the exciter-generator 26. It will then be possible to reduce the speed oi the elevator car I0 to the landing speed necessary to bring it to rest at the floor where the call is registered with the desired degree of accuracy.

When the contact members F2 come into proximity with the inductor plate DF, the previously traced holding circuit for the reversing relay D is opened and it moves to the deenergized position. As a result, the previously traced energizing circuit for the elevator brake releasing winding EW is opened and the brake I8 is applied to the elevator car I. The operating winding of the auxiliary relay N is also deenergized and at contact members NI the energizing circuit for the operating windings of the holding relay J and the ihductors E and F is opened.

A further result of the deenergization of the operating winding of the speed switch His to close contact members H3. A circuit is then completed LI, 5DRI, SDRN, SCD, 49, H3, L2

for energizing the neutralizing winding 5DRN for the call storing relay BDR at the fifth floor. This relay is then restored to the non-operated position.

After the passenger has entered the elevator car IU the operator may then again initiate the movement thereof in the downward direction, at which time the foregoing sequence of starting operation Will be repeated.

lOVr

direction under lightly loaded conditions, it will be apparent that in stopping it acycle of operations similar to that set forth hereinbefore when the car is operated under overhauling load-conditions in the downward direction will take place. Since such a sequence of operation will be readily understood by those skilled in the art Without further description, a detailed description thereof will not be given herein.

Since certain further changes may be made in the foregoingconstruction and diierent embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter shown in the accompanying drawings or set forth in the foregoing description shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In an elevator system, in combination, an

elevator car operable past a plurality of floors, a

generator having driving connection with'said car, a motor electrically connected to be energized by said generator and having a separately excited field winding, an exciter-generator electrically connected to energize said iield winding, common driving means for said motor and exciter-generator disposed to return power to a power source when said car is operated under overhauling load conditions, and means for maintaining the voltage of said exciter-generator available for exciting said motor at a substantially constantv value regardless of said overhauling load conditions.

2. In an elevator system, in combination, an elevator car operable past a plurality of floors, a generator having driving connection with said car, a motor electrically connected to be energized by said generator and having a separately excited eld winding, an exciter-generator electrically connected to energize said iield winding, a driving motor electrically connected to a source of current and mechanically connected to said motor and exciter-generator, said driving motor being disposed to function as a generator when said car is operated under overhauling load conditions, and means for maintaining the voltage of said exciter-generator available for energizing said iield winding at a substantially constant value regardless of said overhauling load conditions.

3. In an elevator system, in combination, an elevator car operable past, a plurality of floors, a generator having drivingk connection with said car, a motor electrically connected to be energized f by said generator and having a separately excited eld winding, an exciter-generator electrically connected to energize said field winding, a driving motor electrically connected to a source of current and having a common shaft connection to said motor and exciter-generator, said driving motor being disposed to function as a generator when said car is operated under overhauling load conditions and at a higher speed than exists when it operates as a motor, and compensating relay means disposed to maintain the voltage of said exciter-generator for energizing said eld winding at a substantially constant value regardless of said overhauling load con- ,A ditions,

4. In an elevator system, in combination, an elevator car operable past aplurality of floors, a generator having driving connection with said car, a motor electrically connected to be ener- ,v gzed by said generator and-having a separately When the elevator, car isV operated in the up excited field winding, an exciter-generator electrically connected to energize said neld winding, an induction motor electrically connected to a Source `of alternating current and mechanically connected to said motor and exciter-generator, said induction motor being disposed to return power to the sourceof alternating current when said car is operated under overhauling load conditions, and compensating relay means disposed to maintain the voltage of said exciter-generator available for energizing said iield winding at a substantially constant value regardless of said overhauling load conditions.

5. In an elevator system, in combination, an

elevator car operable past a plurality of floors,

a generator having driving connection with said car, a motor electrically connected to be energized by said generator and having a separately excited field winding, an exciter-generator con-V nected to energize said eld winding, a generator electrically connected to a source of power and mechanically connected to said motor and exciter-generator, said last named generator being disposed to return power to said source when said car is operated under overhauling load conditions, means for reducing the excitation applied to said field winding from said excitergenerator in response to the registration of a call at a floor thereby causing said motor to drive said exciter-generator at a faster speed under said conditions than it is driven under other operating conditions, and means for maintaining the voltage generated by saidexciter-generator at a substantially constant value to maintain the voltage applied to the circuit of said field winding at a predetermined value regardless of said speed change.

6. In an elevator system, in combination, an elevator car operable past a plurality of oors, a generator having driving connection with said car, a motor electrically connected to be energized by said generator and having a separately excited field winding, an exciter-generator connected to energize said iield winding, a generator electrically connectedv to a source of power and mechanically connected to said motor and exciter-generator, said last named generator beingl disposedl to return power to said source when said car is operated under overhauling load conditions, means for reducing the excitation applied to said eld winding from said exciter-generator in responsev to the registration of a call at a door thereby lcausing said motor to drive said exciter-generator at a faster speed under said conditions than it is driven under other operating conditions, andcompensating relay means connected to be responsive to the voltage generated by said exciter-generator and disposed to maintain thevoltage appliedrto, the circuit of said iield winding at a predetermined value regardless of said speed change.

7. In an elevator system, in combination, an elevator car operable past a pluralityrof floors, a generator having driving connection with said car, a motor electrically connectedto be energizedV Winding from said exciter-generator in response to the registration of a call at a iioor `thereby causing said motor to drive said exciter-generator at a faster speed under said conditions than it is driven under other operating conditions preparatory to stopping said car at the floor, and compensating relay means connected to be responsive to the voltage generated by said excitergenerator and disposed to maintain said voltage t a substantially constant value to provide a Voltage of predetermined value for said eld winding circuit unaffected by said change in speed.

8. In an elevator system, in combination, an elevator car operable past a plurality of floors, a iirst dynamo-electric device having driving connection with said car and disposed to function as a generator when said car is operated under cverhauling load conditions, a second dynamo-electric device electrically connected to said rst dynamo-electric device and disposed to function as a motor under said overliauling load conditions, an exciter-generator electrically connected to separately excite said second dynamoelectric device, a common driving means for said second dynamo-electric device and said excitergenerator disposed to return power to a power source under said overhauling load conditions, and means for maintaining the excitation supplied to said second dynamo-electric device by said exciter generator substantially unaffected by said overhauling load conditions.

9. n an elevator system, in combination, an elevator car operable past a plurality of floors, a iirst dynamo-electric device having driving connection with said car and disposed to function as a generator when said car is operated under overhauling load conditions, a second dynamoelectric device electrically connected to said rst dynamo-electric device and disposed to function as a motor under said overhauling load conditions, an exciter-generator electrically connected to separately excite said second dynamo-electric device, a common driving means for said second dynamo-electric device and said exciter-generator disposed to return power to a power source under said overhauling load conditions, means for reducing the excitation of said second dynamo-electric device in response to the registration of a call at a floor thereby causing said second dynamo-electric device to drive said exciter-generator at a faster speed under said conditions than it is driven under other operating conditions preparatory to stopping said car at the oor, and compensating relay means connected to be responsive to the voltage generated by said exciter-generator and disposed to maintain said voltage at a substantially constant value to provide a voltage of predetermined value for the excitation circuit of said second dynamo-electric device unaiected by said change in speed.

10. In an elevator system, in combination, an elevator car operable past a plurality of doors, a rst direct current dynamo-electric device having driving connection with said car and disposed to function as a generator when said car is operated under overhauling load conditions, a second direct 10 current dynamo-electric device electrically connected to said rst device and disposed to function as a motor under said overhauling load conditions, an exciter-generator electrically connected to separately excite said second device, a shunt field winding for said exciter-generator having a resister connected in series circuit relation therewith, an alternating current dynamo-electric device electrically connected to an alternating current power source and having a common shaft connection to said second device and excitergenerator, said alternating current device being disposed to return power to said power source under said overhauling load conditions, means for reducing the excitation of said second device in response to the registration of a call at a licor thereby causing said second device to drive said exciter-generator at a faster speed under said conditions than it is driven under other operating conditions preparatory to stopping said car at the floor, and compensating relay means connected to be responsive to the voltage generate by said exciter-generator and disposed to vary the effective value of said resistor to maintain said voltage at a substantially constant value to provide a voltage of predetermined value unaffected by said change in speed for exciting said second device.

11. In an elevator control system having a motor for operating an elevator car past a plurality of iioors, in combination, a generator or energizing said motor, the armature of said generator being electrically connected in a loop circuit with the armature of said motor, a separately excited field winding 'for said generator, a self 45 excited exciter-generator electrically connected to energize said field winding, means for driving said generators, means for starting said driving means and for increasing the speed of said generators to operating speed, means for preventing the energization of said eld winding until tne voltage generated by said exciter-generator is at a predetermined Value, and means for maintaining the voltage of Said exciter-generator` substantially at said predetermined value regardless of change in speed of said exciter-generator.

WILLIAM F. EAMES. 

